The invention relates to a high pressure gas discharge lamp having a bulb and a filling which contains a starting gas and a metal compound in such a quantity that in the operational condition of the lamp condensed metal particles are forced which generate light by incandescent emission.
Such a high pressure gas discharge lamp provided with electrodes is known from DE-PS 967 658. Along the metal compounds used are oxides and halides of tungsten and rhenium. This patent describes how a number of the metals listed show a strong, continuous spectrum in the visible range and in the long-wave UV range, especially at higher vapour pressures, so that these metals can be regarded as economic light sources for pure white light. It is also described that some low-volatility, emitting metals can be subject to partial condensation into airborne particles, which then leads to a desired reinforcement of the continued. The metal is returned to its compound in the colder regions of the discharge vessel.
The inner electrodes of the known high pressure gas discharge lamp, however, are attacked by the halides and destroyed in a relatively short period. The oxides cause oxidation of the electrodes, the metal being deposited on the wall of the discharge vessel, so that it does not take part in the discharge anymore. In either case, the result is a very short useful life of the high pressure gas discharge lamp. Moreover, a low degree of condensation in the discharge arc is achieved in the presence of electrodes, because the metal condenses mostly on the relatively cold electrodes.
U.S. Pat. No. 3,720,855 discloses an electrodeless gas discharge lamp having a filling containing an oxytrihalide of vanadium, niobium, or tantalum. The quantity of oxyhalide can have a partial pressure of up to 266 mbar. The lamp emits a line spectrum.